Abstract Most electronic household appliances are packaged with protective buffers to minimise goods damage during transportation and handling. These protective buffers are commonly made from styrofoam, an expandable polystyrene material. The steam injection moulding process is a popular technique used to mass-produce these buffers. In this paper, the development of a PC-based computer-assisted tool for the mould design of these styrofoam buffers is discussed. The algorithmic routines used in the selection of the available machine type, the positioning of the injection guns, ejector pins and steam vents for the mould-making are also highlighted.